1. Field of the Invention
The present invention relates to a video disk on which a television video signal is recorded and it also relates to recording and reproduction devices for the video disk.
2. Background of the Invention
Disks, on which information is recorded at a high density, have been recently developed and put on the market. Typical examples of the disks are a video disk and a digital audio disk. There are a number of types of such video disk and digital audio disk.
A spectrum is recorded on an optical video disk as shown in FIG. 1. A television video signal is recorded on the disk by frequency modulating a carrier to set the sync chip level at 7.6 MHz and the white level at 9.3 MHz. Audio signals such as a right and a left stereo signals and bilingual signals are recorded on the disk by frequency modulating a carrier of 2.3 MHz and a carrier of 2.8 MHz.
The spectrum of EFM (eight-to-fourteen-bit modulation) signals for right and left stereo audio PCM (pulse code modulation) signals recorded on an optical digital audio disk occupies a band below about 2 MHz, as shown in FIG. 2.
Since the band below 2 MHz is almost empty on the video disk as described above, an EFM signal can be subjected to frequency division and multiplexing operation so as to be simultaneously recorded on the video disk. FIG. 3 shows a spectrum in such a case. It is understood from FIG. 3 that each signal can well be separated.
FIG. 4 shows a block diagram of a recording device for such a video disk. A television video signal whose high-band component is subjected to pre-emphasis by a preemphasis circuit 1 is frequency modulated by an FM (frequency modulation) modulator 2 and then entered into an adder 3. Two audio signals in a first pair of channels are pre-emphasized by pre-emphasis circuits 4 and 5, are frequency modulated by FM modulators 6 and 7 and then entered into the adder 3. Audio signals in another pair of channels are subjected to digitization (PCM) by a PCM encoder 8 and to EFM by an EFM encoder 9. An unnecessary high-band component is removed by a low-pass filter 10 and then entered into the adder 3 through a pre-emphasis circuit 11. As a result, the frequency-modulated television video signal, the frequency-modulated audio signals in two channels and the eight-to-fourteen-bit-modulated audio signals in two channels are added together by the adder 3. The output of the adder 3 is multiplexed by a limiter 12 and then supplied to a light modulator 13. Consequently, a laser beam emitted from a laser light source 14 is modulated depending on the input signal to the light modulator 13. A recording medium 17 rotated by a motor 16 is irradiated with the modulated laser beam through an objective lens 15 to record the signal on the medium 17. Since the art of manufacturing the video disk on the basis of the recording medium 17 is well known, this art is not described in detail herein.
FIG. 5 shows a block diagram of a reproduction device for the video disk manufactured as described above. A laser beam emitted from a pickup 23 is irradiated through an objective lens 24 upon the video disk 22 rotated by a motor 21. The laser beam reflected by the disk 22 is received by the pickup 23 through the objective lens 24 to output a reproduced signal. A reproduced RF (radio frequency) signal is sent out from an RF amplifier 25. The video signal FM carrier component of the reproduced RF signal is supplied to an FM demodulator 27 through a band-pass filter 26 so that the component is demodulated and then outputted through a de-emphasis circuit 28. The audio signal FM carrier components of the reproduced RF signal for the first pair of channels are supplied to FM demodulators 31 and 32 through band-pass filters 29 and 30 so that the components are subjected to frequency demodulation by the demodulators 31 and 32 and then outputted through de-emphasis circuits 33 and 34. The EFM signal component of the reproduced RF signal is separated by a low-pass filter 35 and then supplied to a PCM decoder 38 through a de-emphasis circuit 36 and an EFM decoder 37. In the PCM decoder 38, the component is subjected to EFM demodulation and PCM demodulation so that an analog signal is outputted. As a result, the user of the video disk can select the audio signals of high fidelity together with the video signal to achieve high-fidelity listening.
It can be conceived that a digital data signal is recorded as the above-mentioned EFM signal instead of an audio signal. The digital data signal is different from the audio signal in that the digital data signal is not necessarily a continuous signal. For that reason, it can be thought to be advantageous that a block structure is provided for the digital data signal. Whether a reproduction device for the disk is simple or complicated depends on how the positional relation between the block structure and the corresponding video signal is set.